This invention relates to a process and an apparatus for metering liquid colorant or the like. In this specification, the term "liquid colorant" is used in its broadest sense to denote such materials as paint (including clear paint without containing pigment); primary color compound for preparation; liquid paint material such as varnish, dryer or additives; liquid-form dye and ink.
In U.S. Pat. No. 3,349,962 to Herbert C. Levin issued on Oct. 31, 1967, there is disclosed an automatic paint colorant dispensers employing a plurality of reciprocating pumps. Similar attempts have been made and disclosed in U.S. Pat. No. 4,046,287 to Joop F. Hoekstra issued on Sept. 6, 1977, Japanese Patent Public Disclosure No. 100852/78 (corresponding to U.S. Ser. No. 767921) issued on Sept. 2, 1978, German O.S. No. 3007421 to Dotzel Walter issued on Sept. 3, 1981, and U.S. Pat. No. 4,314,653 to Giuseppe Sindoni issued on Feb. 9, 1982.
Paint metering designs in the past often utilized fixed displacement pumps, so they are called "displacement types". In the designs, metering operation has been achieved through an extruding action of the fixed displacement pump. Such metering system of displacement type, however, does not readily lend itself to use for a small amount of paint such as 0.01-0.4 g by weight, resulting in an inconvenience of rather limited accuracy. Another problem is the fact that in order to deal with a plurality of colors and types of paints prior design requires a plurality of fixed displacement pumps corresponding to the number of colors or types of the paint, so that the metering device becomes complicated and color modification can not be easily attained.